A wind turbine transfers the energy of the wind into electrical energy. The wind turbine comprises a nacelle that is connected to a tower and a rotor that is connected to the nacelle. The rotor comprises a hub that is rotatable mounted to the nacelle and at least one rotor blade mounted to the hub.
The wind interacts with the rotor blade of the wind turbine in a way that the rotor rotates. The rotation of the rotor is transferred to an electrical generator.
When the wind turbine is erected, the tower is set up and the nacelle is mounted onto the tower. The hub is mounted to the nacelle and the at least one rotor blade is mounted to the hub.
The at least one rotor blade is hoisted up by a crane and connected to the hub. The hub has to be in a predetermined angular rotational position around his axis of rotation to establish the connection between the hub and the rotor blade.
This position corresponds to the direction of the blade during the fastening of the connection. The position can be a horizontal or a vertical arrangement of the hub and the rotor blade for example.
The hub has to be rotated to establish the connection between the hub and a first rotor blade. In the case of more then one rotor blade that has to be mounted, the position of the hub has to be changed. The hub has to be rotated from the first into a second position to establish the connection between the hub and the second rotor blade.
US 2006/0147308 A1 describes a method of mounting rotor blades to a rotor hub which is connected to a pod of a wind turbine power installation, including the following steps: rotating the rotor hub into a predetermined first position, fitting a rotor blade, rotation the rotor hub via the rotor blade into a predetermined second position, and mounting a second rotor blade, wherein the rotation of the rotor hub is effected in the direction of the effect of gravitational force of the first rotor blade which is already mounted.
This shows a disadvantage that there are no gravitational forces to support the rotation before the connection between the hub and the first rotor blade is established. Furthermore the gravitational force of a first rotor blade will support the rotation into a second position only for a part of the rotation. In a certain second part of the rotation the rotation needs to be performed against the gravitational forces of the first rotor blade. Thus the described method is not reliable enough to perform the rotation of the hub during the installation of the rotor blades.